Ben Paulsen had two hits and drove in a run in his major league debut for the Rockies, who've lost six straight and fell into a tie with Texas for the worst mark in the majors (40-59).

Fister was cruising along until the sixth when the Rockies rallied for two runs on RBI singles from Nolan Arenado and Paulsen to make it 4-2. With the bases loaded and two outs, Nationals manager Matt Williams summoned Aaron Barrett from the bullpen to face pinch hitter Brandon Barnes. Barrett struck out Barnes with a slider in the dirt.

"That was kind of, in my eyes, the turning point in the game," Desmond said.

The Rockies had a little bit of a scare in that inning when Carlos Gonzalez was tagged out trying to slide into third base. He stayed down on the dirt for several minutes, clutching both wrists after jamming them into the ground. Gonzalez had surgery on his left index finger earlier this season and missed more than a month. He stayed in the game, but had a scrape on his right arm.

"I don't know what else can happen this year," Gonzalez said.

Washington padded its lead in the seventh on an RBI single from Wilson Ramos. Desmond later scored on a wild pitch.

Colorado was missing several big bats from its lineup as Troy Tulowitzki missed a second straight game with a sore left thigh. Earlier in the day, Justin Morneau was placed on the 15-day disabled list with a strained neck.

Taking Morneau's place at first was Paulsen, who was called up from Triple-A Colorado Springs. He's the ninth different player to make his debut with the team in 2014.

Paulsen lined a single to left in his first plate appearance. After Fister received the ball on the mound, he tossed it to a bat boy as a keepsake for Paulsen.

Washington finally solved Morales in the fourth, scoring four times. Desmond gave Fister all the run support the right-hander would require with a two-run homer to left.

Danny Espinosa drove in another run with a double and later scored when Morales tried to pick off Fister at first and threw the ball down the right-field line.

Blackmon led off the first with a double, but Fister managed to escape. Fister struck out Gonzalez with a 79-mph changeup to end the inning.

"You know you have to keep the ball down," Fister said. "That's something we focused on a lot tonight."

Game notes

Williams called OF Bryce Harper's day off "a one-day thing." Harper entered as a pinch hitter in the seventh and struck out, then briefly argued with the home-plate umpire over whether he foul tipped the pitch. Williams pulled Harper away. ... RHP Jordan Zimmermann (6-5), who left his last start with a cramp in his right biceps, will start Tuesday. The Rockies will throw LHP Yohan Flande (0-2). ... A woman was hit in the head when the bat slipped out of Gonzalez's hands in the fourth. She was escorted from her seat.